1. Field of the Invention
The present invention relates to sockets for use in connecting semiconductor chip assemblies to substrates and the methods of making such sockets.
2. Description of the Related Art
U.S. patent application Ser. No. 08/254,991 filed on Jun. 7, 1994, the disclosure of which is incorporated herein, discloses a connector for mounting a microelectronic element to a substrate. In certain embodiments, the connector includes a sheet-like dielectric body having a plurality of holes, an array of resilient contacts secured to the dielectric body and an array of terminals electrically connected to the contacts.
U.S. Pat. No. 5,632,631, which issued on May 27, 1997, the disclosure of which is incorporated herein, discloses, in certain embodiments, a contact comprising a base portion and a plurality of asperities protruding upwardly from the surface of the base portion. The base portion may include a ring-like anchor region and a plurality of tabs extending inwardly from the anchor region to a common center. The asperities may be disposed on the tabs. The ""631 patent also discloses a connector which includes a connector body and at least one of the contacts described above and wherein the anchor region of each contact is fixed to the connector body and the tabs are free to bend. When a mating contact element (such as a lead or solder ball) is forced against the contact, the tabs bend and the mating contact element is wiped across the asperity causing the sharp edges of the asperity to scrape the mating contacting element so that an electrical connection to the mating contact element can more easily be made.
U.S. Pat. No. 5,615,824, which issued on Apr. 1, 1997, the disclosure of which is incorporated herein, discloses a method of making an electrical connection. In a preferred embodiments, the method comprises the steps of engaging a first element having a plurality of solder masses and a second element having a plurality of resilient contacts; heating the elements so that the contacts penetrate the solder masses; and cooling the assembly. The second element may be comprised of a connector body having a plurality of holes. Each resilient contact may have one or more tabs which project over one of such holes. The tabs bend during the engaging step and spring back as the contacts penetrate the solder masses. Each contact may be covered by a solder mask made of a dielectric material that is a thermoplastic.
Certain embodiments disclosed in U.S. patent application Ser. No. 08/862,151, filed on May 22, 1997 disclose a connector for a microelectronic assembly which includes a sheetlike body having a plurality of contacts, a substrate having leads, and a support structure extending between sheetlike element and the substrate. The contacts may include several sheetlike metallic projections extending inwardly around a hole in the sheetlike element one side of the sheetlike element. A support structure, such as an array of non-collapsing structural posts is on another side of the sheetlike element. Each of the contacts is surrounded by several posts. The posts keep the sheetlike element spaced away from a substrate to which the posts are attached. The disclosure of the ""151 application is incorporated herein.
Many of the sockets described in the disclosures set for above as well as many other sockets of the prior art rely upon pressure to maintain an electrical contact between the device to be tested and the contacts of the socket. A lid or other backing element is placed over the device and pressure is applied to the lid to insure that the electrical contact between the device and the contacts on the socket are maintained. Some sockets may, in the alternative or in addition, have a mechanism for engaging the sides of the chip or the device. While the above mentioned socket designs are important improvements to socket technology, further improvements are desirable.
The present invention relates to methods of using sockets for connecting a semiconductor chip assembly to an external substrate such as a printed circuit board. Such semiconductor chip assemblies have a plurality of electrically conductive joining units such as bumped leads or ball leads. Semiconductor chip assemblies which may be connected to an external substrate using the socket of the present invention include, for example, flip chip assemblies, ball grid arrays and assemblies, such as those disclosed in commonly assigned U.S. Pat. Nos. 5,148,265 and 5,148,266. The semiconductor chip assembly may comprise a single semiconductor chip, a plurality of semiconductor chips or wafer. The socket of the present invention can be used to permanently connect a semiconductor chip assembly to an external substrate, such as a printed circuit board; or to temporarily connect such an assembly to an external substrate, such as a test circuit board, for testing purposes. The socket of the present invention incorporates a grabbing or locking feature that is capable of capturing the joining units of the chip assembly. In certain embodiments, the socket of the present invention is lidless because it does not require a lid or any other mechanism for applying pressure to a semiconductor chip assembly in order to maintain an electrical contact between the terminals of the chip assembly and the socket.